The invention relates to an engine power section for piston engines, particularly V-engines.
For reducing the weight of an engine power section, it is basically known to manufacture the power unit block, which is highly loaded and is essentially formed of the cylinders with directly or indirectly shaped-on crankshaft bearings, preferably of an iron material, and to construct the less loaded power section walls separately of a lighter material or one which is manufactured with a particularly thin wall.
One example of this construction principle for the engine power section of a liquid-cooled internal-combustion engine is known from British Patent Document GB-PS 678 903, in which case the power section walls adjoining the crank space as well as the power section walls used for covering the cylinder coolant spaces are made of metal sheets. In contrast, for achieving the required stability, the power unit block has a relatively massive construction with end-side front walls between the cover plates and base plates of the cylinders, heavy bearing blocks being arranged in one piece on the base plate.
Disadvantages of this known engine power section and of the engine power section known from British Patent Document GB-PS 695 972 are in each case a moderate weight reduction as well as corrosion and sealing problems, particularly in the connection points of the structural components made of different materials. In addition, there are problems concerning acoustics.
For reducing particularly the acoustic problems, an engine power section for a liquid-cooled internal-combustion engine is known from U.S. Pat. No. 4,446,827 which comprises a power unit block which has a massive design corresponding to the above-mentioned British Patent Document GB-PS 678 903, to which separate power section walls are assigned which are made of a very sound-absorbing material, such as rubber, plastic or resin.
According to German Registered Utility Patent DE-U 94 12 637, corrosion and sealing problems for an engine power section of a liquid-cooled internal-combustion engine designed of different materials is avoided in that a light-metal power section is poured around a power unit block made of gray cast iron, the coolant spaces being constructed exclusively in the light metal power section. A disadvantage in this case is the massive design of the power unit block with engine baseboards arranged on the crankshaft bearing blocks by way of web-type supports, which baseboards are connected with the light metal power section in a material-locking manner in the oil pan connection area of the light metal power section. This heavy design results in another disadvantage in that these engine baseboards connected in a material-locking manner with the bearing blocks act as structure-borne noise bridges and acoustically excite at least the crank space covers of the light metal power section which are connected with them in a material-locking manner.
Further, from European Patent Document EP-A 0 554 575, which was published before German Patent Document DE-U 94 12 637, an engine power section for a liquid-cooled internal-combustion engine is known in the case of which a power unit block also made of gray cast iron is cast into a light metal power section. For reducing the weight of the power unit block, cylinders arranged in a row are arranged in a material-locking adjacent manner and carry massively designed bearing blocks arranged by way of spaced flat webs in the connection areas. During the casting into the light metal power section, the flat webs and the bearing blocks are integrated in a material-locking manner in transverse walls connected with the light metal power section. This support of the crankshaft bearings with respect to a crank space power section wall which is designed for reasons of stability and requires high expenditures of material acts as a structure-born sound bridge which acoustically excites the light metal power section.
Finally from Japanese Published Patent Application 4-121 443, a power unit block is known for a liquid-cooled internal-combustion engine which has a shaped-on cylinder head. This design, which is known as a "monoblock", comprises a base plate which is constructed at the lower end of the cylinder bushes and on which, on the one hand, a casing is detachably fastened which surrounds the monoblock and on which, on the other hand, massively constructed crankshaft bearing blocks are arranged whose bearing caps are arranged by way of longitudinal webs in a bearing frame which disadvantageously is designed to require high expenditures of material.
The characteristic which the above-indicated state of the art has in common is the fact that resistance to bending and torsion required for a power unit block is achieved predominantly by way of cylinders which are connected with one another, specifically either by their siamese-type attached arrangement or their arrangement between cover and base flange plates connected in one piece in a material-locking manner which, in addition, are connected by way of front plates.
The above-mentioned type-forming Japanese Published Patent Application 4-121 443 shows a particularly stiff power unit block which, however, is also heavy because of the cylinder head which is provided instead of the cover flange plate and which is arranged in a one-piece material locking manner, which power unit block has a massive bearing frame for the bearing caps of the crankshaft bearings.
It is an object of the invention to provide a light weight power unit block with cylinders which has a high design stability which is insignificantly increased by the cylinders, for a light-weight engine power section.
This object is achieved by arranging the flange plate to be offset relative to the cylinder from its lower end to its upper end with its face-side surface center of gravity at a distance on this side of the bearing center plane of the crankshaft bearings, which corresponds at least to a largest possible distance of the surface center of gravity of a profile of the stiffening element of the bearing frame on the other side of the bearing center plane, the crankshaft bearings being connected by way of struts with the flange plate.
It is the basic idea of the invention to arrange devices of the power unit block arranged in the longitudinal direction of the engine relative to the axis of rotation of the crankshaft at the largest possible distance in a connection or achieving a high moment of inertia and thus a high moment of resistance, in which case the effective distances required for this purpose are, on the one hand, achieved by way of the design of the bearing frame with at least one stiffening element provided particularly low below the crankshaft and, on the other hand, by a flange plate which is advantageously easily arranged to be displaced at a far distance in the direction of the vertical axis of the cylinder or cylinders from the axis of rotation of the crankshaft. As the result of the flange plate integrated according to the invention with the stiffening element of the bearing frame in a connection, the cylinder as the element providing significant stability is eliminated, whereby the cylinder or cylinders can advantageously be constructed to have a thin wall.
In addition, by means of the invention, the piston stroke and the cylinder diameter can be defined without taking into account the design stability of the power unit block, with the advantage that also large-volume, high-power piston engines can be constructed to be relatively low. With the free selection of the largest possible distances of devices pointing in the longitudinal direction of the engine from the plane of the axis of rotation of the crankshaft, the invention offers the advantage with respect to a light construction of the power unit block that these devices (flange plate, stiffening elements) can have a relatively thin-walled design while the stability is high.
Advantageous further developments of the engine power section according to the invention achieve a high design stability of both structural components individually and in a functional connection by means of open and hollow profiles which are connected with one another in a one-piece material-locking manner for the power unit block manufactured preferably of gray cast iron as well as for the casing made of light metal which is in one piece with the power section walls in each case at low expenditures of material.